The present disclosure relates to toners and processes useful in providing toners suitable for electrophotographic apparatuses, including apparatuses such as digital, image-on-image, and similar apparatuses. In particular, the present embodiments are directed to a process for making toners that increases the charge of the toner particles, and toners made from the same.
Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. These toners are within the purview of those skilled in the art and toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Toner systems normally fall into two classes: two component systems, in which the developer material includes magnetic carrier granules having toner particles adhering triboelectrically thereto; and single component systems (SDC), which may use only toner. Placing charge on the particles, to enable movement and development of images via electric fields, is most often accomplished with triboelectricity. Triboelectric charging may occur either by mixing the toner with larger carrier beads in a two component development system or by rubbing the toner between a blade and donor roll in a single component system.
Charge control agents (CCA) may be utilized to enhance triboelectric charging. Charge control agents may include organic salts or complexes of large organic molecules. Such agents may be applied to toner particle surfaces by a blending process. Such charge control agents may be used in small amounts of from about 0.01 weight percent to about 5 weight percent of the toner to control both the polarity of charge on a toner and the distribution of charge on a toner. Although the amount of charge control agents may be small compared to other components of a toner, charge control agents may be important for triboelectric charging properties of a toner. These triboelectric charging properties, in turn, may impact imaging speed and quality, as well as allow for extended life performance. Examples of charge control agents include those found in EP Patent Application No. 1426830, U.S. Pat. No. 6,652,634, EP Patent Application No. 1383011, U.S. Patent Application Publication No. 2004/0002014, U.S. Patent Application Publication No. 2003/0191263, U.S. Pat. No. 6,221,550, and U.S. Pat. No. 6,165,668, the disclosures of each of which are totally incorporated herein by reference.
One issue that may arise with charge control agents is that they are difficult to incorporate into emulsion aggregation toners. Generally, during incorporation some charging properties are lost. Namely, the charging property is no longer evident when the additive package is added to the particle, causing a drastic decrease in charge and thus ultimately impacting life performance of the toner.
Moreover, current toner formulations show that charging is zone specific, performing with stability in B zone and J Zone but worsening in A Zone. Through the addition of a shell to the toner particle, passivation of the pigments is possible but if a charge control agent is added to the core, shell or both, the charge control agent tends to create inhomogeneity of the charging. This is due to the fact that the addition of charge control agents in the shell tends to cause non-homogenous distribution of the charge control agent, and thus, leads to inhomogeneity of the charging. Compounding the problem is the fact that high amounts of residual surfactant also contribute to zone variability in the charging. Because most emulsion aggregate toner is made with nano-sized pigment, wax and latex, all of these substituents must be dispersed using high surfactant levels. An issue with this method is that too much surfactant causes issues with zone charging from J zone to A zone to B zone.
Thus, improved methods for producing toner, which permit excellent control of the charging of toner particles, remain desirable.